Typical coaxial cable includes radio frequency (RF) shielding. One common type of shielding is a conductive tape that attenuates interfering electromagnetic fields in the high frequency range.
With reference first to FIG. 1A, a prior art coaxial cable 100 is disclosed. As disclosed in FIG. 1A, the coaxial cable 100 is terminated on either end with connectors 150. With reference now to FIG. 1B, the prior art coaxial cable 100 generally includes a center conductor 102 surrounded by a dielectric 104, a tape 106 wrapped longitudinally around the dielectric, a braid 108 surrounding the tape 106, and a jacket 10 surrounding the braid 108.
With reference now to FIG. 1C, the tape 106 surrounds the dielectric 104, and generally serves to limit the ingress and egress of high frequency electromagnetic fields 126 to/from the center conductor 102. The tape 106 is a laminate tape that includes a first aluminum layer 112, a polymer layer 114, a second aluminum layer 116, and a polymer bonding agent layer 118. The tape 106 also defines a first edge portion 120 that overlaps a second edge portion 124 as the tape 106 is longitudinally wrapped around the longitudinal direction of the dielectric 104, resulting in an overlapping seam that runs parallel to the center conductor 102.
With continuing reference to FIG. 1C, and with reference also to FIG. 1D, a common problem with the tape 106 of the prior art coaxial cable 100 is disclosed. In particular, although the first and second aluminum layers 112 and 116 are generally effective at shielding high frequency electromagnetic fields 126 above the frequency for one skin depth, since the polymer layer 114 and the polymer bonding agent layer 118 are formed from dielectric materials, the layers 114 and 118 are not effective at shielding electromagnetic fields 126. As a result, some high frequency electromagnetic fields 126 from the center conductor 102, such as electromagnetic fields greater than about 50 MHz, exit the prior art coaxial cable 100 by traveling through an overlap aperture 128 of the polymer bonding agent layer 118.
Similarly, although the second aluminum layer 116 is generally effective at shielding electromagnetic fields 126 above the frequency for one skin depth, some fraction of the high frequency electromagnetic fields 126 from the center conductor 102 do pass through the second aluminum layer 116. This results in some high frequency electromagnetic fields 126 from the center conductor 102 exiting the prior art coaxial cable 100 by traveling through an overlap aperture 130 of the polymer layer 114. These high frequency electromagnetic fields 126 that exit the prior art coaxial cable 100 cause harmful interference with surrounding electrical equipment (not shown). Some high frequency electromagnetic fields from surrounding electrical equipment (not shown) also enter the prior art coaxial cable 100 through the overlap apertures 128 and 130, thus causing harmful interference with data signals that are traveling through the center conductor 102.
With reference now to FIG. 1E, another prior art coaxial cable 100′ is disclosed. The coaxial cable 100′ is identical to the coaxial cable 100 except that the coaxial cable 100′ includes a helically wrapped tape 106′. As disclosed in FIG. 1E, the tape 106′ also defines a first edge portion that overlaps a second edge portion as the tape 106′ is helically wrapped around the dielectric 104, resulting in an overlapping seam that runs in a spiral configuration around the dielectric 104. As with the tape 106, the tape 106′ allows some high frequency electromagnetic fields to enter/exit the coaxial cable 100′ by traveling through one or more overlap apertures. These high frequency electromagnetic fields cause harmful interference with surrounding electrical equipment (not shown) and with data signals that are traveling through the center conductor 102.